Diverterless supersonic inlet

The Lockheed Martin F-35 Lightning II is a major jet fighter design featuring DSI.

A diverterless supersonic inlet (DSI) is a type of jet engine air intake used by some modern combat aircraft to control air flow into their engines. It consists of a "bump" and a forward-swept inlet cowl, which work together to divert boundary layer airflow away from the aircraft's engine. This eliminates the need for a splitter plate, while compressing the air to slow it down from supersonic to subsonic speeds. The DSI can be used to replace conventional methods of controlling supersonic and boundary-layer airflow.

DSIs can be used to replace variable-geometry intake ramp and inlet cone, which are more complex, heavy and expensive.[1]

Technical background

Testing of the F-35 diverterless supersonic inlet on a modified F-16. The original intake is shown in the top image.

The fundamental design of a gas turbine engine is such that the air flow-rate entering its compressor is regulated by the amount of fuel burned in its combustor. For supersonic flight the air entering the inlet also has to be regulated to a similar amount by the design of the entrance of the inlet duct. The optimum design of the duct will minimize drag on the one hand and unstable shock position (manifested by "buzz") on the other, while presenting clean and uniform airflow to the fan and compressor.[2]

Inlets

The goal of an engine inlet is to present clean and uniform airflow with minimal distortion to the engine. When a body, such as a wing or a fuselage, passes through a fluid such as the air, a boundary layer of fluid attaches to the body and moves along with it. This boundary layer is turbulent and thickens with increasing airspeed and forebody distance. When it enters the inlet, it can cause airflow distortion and affect engine operation and performance. To prevent the boundary layer from entering the engine, inlets typically incorporate a splitter plate to separate the layer, or a bleed system to remove it by suction, or a combination of both.[2]

Additionally, on supersonic jets, the high kinetic energy in the approaching air, or dynamic pressure, has to be transformed into static pressure while losing a minimum amount of energy (also known as pressure recovery). To do this the inlets are more complicated than subsonic ones as they have to set up two or three shock waves to compress the air. A cone or inclined ramp protrudes ahead of the inlet and is adjusted based on flight conditions, thus having variable geometry, to properly position the shocks with the cowl, thus ensuring stable operation and efficient pressure recovery. The complexity of these variable-geometry inlets increases with increase in design speed. Simpler fixed-geometry pitot-type inlets (such as those found on the F-16 and F/A-18) avoid these complexities, thus reducing weight and cost, but have poorer pressure recovery particularly at higher Mach numbers.[2]

Diverterless inlets

J-10B with a diverterless air intake displayed at Airshow China 2018

The DSI bump functions as a compression surface and creates a pressure distribution that prevents the majority of the boundary layer air from entering the inlet at speeds up to Mach 2. The bumped surface create a spanwise static pressure gradient that diverts the boundary layer; this bump also performs flow compression at supersonic speeds. The forward-swept cowl then allows the diverted boundary layer to spill out of the sides of the inlet, preventing much of it from entering the inlet. In essence, the DSI does away with complex and heavy mechanical systems for boundary layer control and pressure recovery with no moving parts.[3]

History

Initial research into the concept was done by Antonio Ferri in the 1950s and was then known as the "Ferri scoop"; it was incorporated in some supersonic designs such as the XF8U-3 Crusader III and the SSM-N-9 Regulus II.[4] The concept was further developed & optimized by Lockheed Martin in the early 1990s using computational fluid dynamics (CFD) and was subsequently termed "diverterless supersonic inlet" (DSI).[5] The first Lockheed DSI was flown on 11 December 1996 as part of a Technology Demonstration project. It was installed on an F-16 Block 30 fighter, replacing the aircraft's original pitot-type intake that included a diverter. The modified F-16 demonstrated a maximum speed of Mach 2.0 (the F-16's clean certified maximum speed) and handling characteristics similar to a normal F-16 with no engine stalls or anomalies, validating CFD predictions. It was also shown that pressure recovery was comparable at transonic speeds and superior at supersonic speeds; subsonic specific excess power was also slightly improved.[3][1]

The DSI concept was introduced into the JAST/JSF program as a trade study item in mid-1994. It was compared with a traditional "caret" style inlet. The trade studies involved additional CFD, testing, and weight and cost analyses.[2] A DSI was incorporated into the design of the Lockheed Martin F-35 Lightning II in 2000 after proving to be 30% lighter and showing lower production and maintenance costs over traditional inlets while still meeting all performance requirements.[1][3]

Benefits

Weight and complexity reduction

Traditional aircraft inlets contain many heavy moving parts for diverting the boundary layer and/or ensuring efficient pressure recovery during supersonic flight. In comparison, DSI eliminates all moving parts, which makes it far less complex and more reliable than earlier diverter-plate inlets. The removal of moving parts also reduces the weight of the aircraft.[6]

Stealth

DSIs improve the aircraft's very-low-observable characteristics by eliminating radar reflections between the diverter and the aircraft's skin.[1] Additionally, the "bump" surface reduces the engine's exposure to radar, significantly reducing a strong source of radar reflection[7] because they provide an additional shielding of engine fans against radar waves.

Analysts have noted that the DSI reduces the need for application of radar-absorbent materials in reducing frontal radar cross section of the aircraft.[1][8]

List of aircraft with DSI

Active

Future

See also

References

  1. ^ a b c d e Hehs, Eric (15 July 2000). "JSF Diverterless Supersonic Inlet". Code One magazine. Lockheed Martin. Retrieved 11 February 2011.
  2. ^ a b c d Hamstra, Jeffrey W.; McCallum, Brent N. (15 September 2010). Tactical Aircraft Aerodynamic Integration. doi:10.1002/9780470686652.eae490. ISBN 9780470754405. Archived from the original on 19 October 2021. Retrieved 19 October 2021.
  3. ^ a b c Chris Wiegand; Bruce A. Bullick; Jeffrey A. Catt; Jeffrey W. Hamstra; Greg P. Walker; Steve Wurth (13 August 2019). "F-35 Air Vehicle Technology Overview". American Institute of Aeronautics and Astronautics. Progress in Astronautics and Aeronautics. 257: 121–160. doi:10.2514/5.9781624105678.0121.0160. ISBN 978-1-62410-566-1.
  4. ^ US Expired US2990142A, Antonio Ferri, "Scoop-type supersonic inlet with precompression surface", published 27 June 1961, issued 27 June 1961 
  5. ^ Saheby, Eiman B; Shen, Xing (2019). "Design and performance study of a parametric diverterless supersonic inlet". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 234 (2). Institution of Mechanical Engineers: 470–489. doi:10.1177/0954410019875384. Retrieved 15 August 2025.
  6. ^ "F-35 JSF Technology". Archived from the original on 2012-05-06. Retrieved 2015-06-04.
  7. ^ ""Fast History: Lockheed's Diverterless Supersonic Inlet Testbed F-16"". Archived from the original on 2013-09-07. Retrieved 2023-08-07.
  8. ^ "J-20's Stealth Signature Poses Interesting Unknowns" Archived 2013-05-15 at the Wayback Machine. Aviation Week. Retrieved 13 January 2013
  9. ^ "歼-10B改进型". AirForceWorld.com. Archived from the original on 2013-08-05. Retrieved 2013-08-01.
  10. ^ "JL-9 Trainer Jet gets DSI inlet, Guizhou China". AirForceWorld.com. Archived from the original on 5 August 2013. Retrieved 29 Aug 2011.
  11. ^ "Paris Air Show 2011 - Naval air trainer unveiled by Chinese media". home.janes.com, 15 February 2012.
  12. ^ "AMCA could fly undetected during dangerous missions". Onmanorama. February 5, 2020. Retrieved 2020-02-06.
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